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4              MOBPHOLOGY AND EVOLUTION
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tioned by zoologists, whereas the Dutch settlers believe there is only one. The skull of this animal varies continually throughout life, and this may account for the differences in the external appearances upon which classifications are founded. It is therefore evident that the characters of a species can only be accurately defined after some hundreds of representatives have been examined.
Problems of Distribution.—The present-day Anthropoids are restricted to the dense forests in the tropical parts of Asia and Africa, but the discovery of the remains of extinct forms (e.g., Dryopitliecus, Plio-pitfMCiw> Pateopithecus, &c.) in the rocks of France, Germany and Northern India shows that the distribution was fornieiiv wider. We can assume that their extinc-
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tion in these regions was probably due to climatic factors. Endocrine Glands and Evolution.—Much light has been thrown on the relations between Man and the Apes by studies of the functions and diseases of the endocrine organs or ductless glands. And a study of these organs enables us to understand some of the agencies which have moulded the characters of the various human races. At a certain stage the foetuses of the Apes and Man have many characters in common, but the subsequent developmental changes, both intra-uterine and extra-uterine, proceed in different directions. In the Apes they are marked by a progressive increase in certain parts, such as the cutaneous pigmentation, hair, limbs, and facial skeleton. In Man, on the other hand, they are characterized by suppression, but the power to develop further lies dormant. The suppressive agents are the various ductless glands. When they are